Hybrid mounting system for pollution control devices

ABSTRACT

A pollution control device has a metal housing, a solid pollution control device disposed within the metal housing, and a mounting mat disposed between the pollution control element and the housing for positioning the pollution control element and for absorbing mechanical and thermal shock. The mounting mat includes a layer of intumescent material having at least one insert formed of a resilient, flexible, fibrous non-intumescent material. The insert is positioned along at least a portion of at least one lateral edge of the mounting mat to prevent erosion of the intumescent material and to provide a seal between the pollution control element and the housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 09/270,139, filedMar. 16, 1999, issued as U.S. Pat. No. 6,613,294, which is acontinuation of U.S. Ser. No. 08/666,735, filed Jun. 18, 1996, issued asU.S. Pat. No. 5,882,608.

BACKGROUND OF THE INVENTION

The present invention relates to pollution control devices, andparticularly to catalytic converters and diesel particulate filters ortraps for an automotive exhaust system. The pollution control devicestypically comprise a metal housing with a monolithic element securelymounted within the casing by a resilient and flexible mounting mat. Themounting mat is comprised of an intumescent sheet material havinginserts formed of a non-intumescent ceramic fiber composite.

Pollution control devices are universally employed on motor vehicles tocontrol atmospheric pollution. Two types of devices are currently inwide spread use—catalytic converters and diesel particulate filters ortraps. Catalytic converters contain a catalyst, which is typicallycoated on a monolithic structure mounted in the converter. Themonolithic structures are typically ceramic, although metal monolithshave been used. The catalyst oxidizes carbon monoxide and hydrocarbons,and reduces the oxides of nitrogen in automobile exhaust gases tocontrol atmospheric pollution. Due to the relatively high temperaturesencountered in these catalytic processes, ceramics have been the naturalchoice for catalyst supports. Particularly useful catalyst supports areprovided by ceramic honeycomb structures as described, for example, inU.S. Pat. No. Re. 27,747.

More recently, catalytic converters utilizing metallic catalyst supports(metallic monoliths) have also been used for this purpose. (See forexample, in U.K. Patent No. 1,452,982, U.S. Pat. No. 4,381,590 and SAEpaper 850131).

The most common diesel particulate filters or traps are monolithicwall-flow filters. These monolithic wall-flow type diesel particulatefilter elements are typically comprised of honeycombed, porous,crystalline ceramic (e.g., cordierite) material. Alternate cells of thehoneycombed structure are typically plugged such that exhaust gas entersin one cell and is forced through the porous wall of one cell and exitsthe structure through another cell. The size of the diesel particulatefilter element depends on the particular application needs. Usefuldiesel particulate filter elements are commercially available, forexample, from Corning Inc. of Corning, N.Y., and NGK Insulator Ltd. ofNagoya, Japan. Useful diesel particulate filter elements are discussedin “Cellular Ceramic Diesel Particulate Filter,” Howitt et al., PaperNo. 810114, SAE Technical Paper Series, 1981.

In the state of the art construction of these devices, each type ofdevice has a metal housing which holds within it a monolithic structureor element that can be metal or ceramic, and is most commonly ceramic.The monolithic structure is mounted in the housing in a process referredto as canning. There is a gap or space between the monolith and thehousing which varies because there is a range of size tolerances forboth the monolith and the housing. The largest gap exists when themonolith is on the small end of the range and the housing is on thelarge end of the range. To avoid damage to the monolith and to hold itin place a mounting material, such as an intumescent mounting mat or anintumescent paste, is typically disposed around the monolith beforecanning. The mounting material fills the gap. After the wrapped monolithis inserted into the housing, the can is pressed closed and flangesalong the lateral edges of the housing are welded. After installation onthe vehicle, the pollution control device is heated by the hot exhaustgases which expand the intumescent materials generating additionalholding pressure. The amount of pressure is determined by the mountdensity of the materials and the temperatures of use. If the mountdensity is too low, there will be insufficient pressure to hold themonolith in place. If the mount density is too high, excessive pressurecan be exerted by the mounting material between the housing and themonolith causing deformation of the housing and/or damage to themonolith.

After the monolith has been secured in the housing, the intumescentmounting material serves to avoid or reduce damage from other conditionsthat can be problematic to the pollution control device. The device canbe subjected to damaging vibrations both before and after installationin a vehicle. Additionally, the entire device is subjected to elevatedtemperatures, e.g., over 300° C., for various periods of time.

A ceramic monolith has a coefficient of thermal expansion generally anorder of magnitude less than the metal (usually stainless steel) housingin which it is contained, so that at elevated temperatures, the mountingmaterials must expand sufficiently to compensate for the differentialexpansion, but not so much as to create excessive pressure which candamage the housing or the monolith. The mounting material also preventshot exhaust gases from passing between the monolith and the metalhousing (thereby bypassing the catalyst).

Typically, the mounting materials include inorganic binders, inorganicfibers that may also serve as a binder, intumescent materials, andoptionally, organic binder, fillers and other adjuvants. The materialsare used as pastes, sheets, and mats. Ceramic mat materials, ceramicpastes, and intumescent sheet materials useful for mounting the monolithin the housing are described in, for example, U.S. Pat. No. 3,916,057(Hatch et al.), U.S. Pat. No. 4,305,992 (Langer et al.), U.S. Pat. No.4,385,135 (Langer et al.), U.S. Pat. No. 5,254,410 (Langer et al.), U.S.Pat. No. 5,242,871 (Hashimoto et al.), U.S. Pat. No. 3,001,571 (Hatch),U.S. Pat. No. 5,385,873 (MacNeil), U.S. Pat. No. 5,207,989 (MacNeil),and Great Britain Patent 1,522,646 (Wood).

U.S. Pat. No. 4,999,168 to TenEyck describes a crack resistantintumescent sheet having a preformed intumescent layer adhesively bondedto a reinforcing layer of a sheet material such as craft paper, plasticfilm, inorganic fabric.

U.S. Pat. No. 4,865,818 to Merry et al. describes a method of producinga catalytic converter by wrapping a thin sheet of mat material aroundthe monolith at least twice in a layer wise fashion.

U.S. Pat. No. 4,929,429 to Merry describes a composite for catalyticconverters having a ceramic fiber mat stitched-bonded to an intumescentmat material.

U.S. Pat. No. 4,048,363 to Langer et al. describes a composite having atleast two layers of similar sheets of intumescent materials.

As the pollution control device is cycled between high and lowtemperatures, the size of the gap between the monolith (metal orceramic) and the housing continuously changes, and the mounting mat isrepeatedly compressed and uncompressed. In cases where the housingreaches very high temperatures, i.e., greater than about 700° C.,deformation of the housing can occur. In these cases, conventionalintumescent mat mounting material may lack the high temperatureresiliency to provide continued support for the monolith. A need thusexists for a mounting system which is sufficiently resilient andcompressible to accommodate the changing gap between the monolith andthe metal housing without causing deformation of the metal housing.Further, while the state of the art mounting materials have their ownutilities and advantages, there remains an ongoing need to improvemounting materials for use in pollution control device. Additionally, itwould be desirable to provide materials that function well over abroader temperature range.

SUMMARY OF THE INVENTION

The present invention provides a hybrid mounting system for pollutioncontrol devices which utilize a monolith structure within a metalhousing. The mounting system comprises a mounting mat disposed betweenthe monolith and the metal housing of the pollution control device. Themounting system includes one or more inserts formed of a resilient,flexible, fibrous non-intumescent material positioned alongside aperipheral or a lateral edge of the mounting mat. In a preferredembodiment, the mounting mat is an intumescent material, and theresilient, flexible, fibrous insert is formed of a non-intumescentmaterial. The hybrid mounting mat is useful for protecting fragilemonolithic structures in catalytic converters, diesel particulatefilters, and high temperature filters. The hybrid mounting mat offersthe advantage of being able to combine the properties of the intumescentmounting mat and the non-intumescent inserts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exploded view of a catalytic converter showingthe mounting system of the present invention.

FIG. 2 is a view of the catalytic converter of FIG. 1, showing themounting system of the present invention peeled away from the monolith.

FIG. 3A shows a prior art bonding system comprised of an intumescentmaterial.

FIG. 3B shows the mounting system of FIG. 3 a disposed about a monolith.

FIG. 4A shows a preferred embodiment of the mounting system of thepresent invention.

FIG. 4B shows the mounting system of FIG. 4 a disposed about a monolith.

FIG. 5A shows an alternative embodiment of a mounting system of thepresent invention.

FIG. 5B shows the mounting system of FIG. 5 a disposed about a monolith.

FIG. 6A shows an alternative embodiment of a mounting system of thepresent invention.

FIG. 6B shows the mounting system of FIG. 6 a disposed about a monolith.

FIG. 7A shows an alternative embodiment of a mounting system of thepresent invention.

FIG. 7B shows the mounting system of FIG. 7 a disposed about a monolith.

FIG. 8A shows an alternative embodiment of a mounting system of thepresent invention.

FIG. 8B shows the mounting system of FIG. 7 a disposed about a monolith.

FIG. 9 shows an alternative embodiment of a catalytic converter having adual monolith.

FIG. 10 shows an alternative embodiment of the mounting system of thepresent invention.

FIG. 11 shows yet another alternative embodiment of the mounting systemof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the mounting system of the present invention is suitable foruse in a variety of pollution control devices, such as catalyticconverters and diesel particulate filters or traps, its use is describedherein in connection with a catalytic converter. The description isintended to be illustrative of the use of the mounting system of thepresent invention and should not be construed as limiting the use of themounting system to catalytic converters.

Referring now to FIGS. 1 and 2, catalytic converter 10 comprisesmetallic housing 12 with generally conical inlet 14 and outlet 16. Thehousing, which is also referred to as a can or a casing, can be madefrom suitable materials known in the art for such use and is typicallymade of metal. Preferably, the housing is made of stainless steel.

Disposed within housing 12 is a monolithic catalytic element 20 formedof a honeycombed monolithic body either of ceramic or metal. Suitablecatalytic converter elements, also referred to as monoliths, are knownin the art and include those made of metal or ceramic. The monoliths orelements are used to support the catalyst materials for the converter. Auseful catalytic converter element is disclosed, for example, in U.S.Pat. No. RE 27,747 (Johnson). Monolith 20 has a plurality of gas flowchannels (not shown) therethrough. The catalyst materials coated ontothe catalytic converter elements include those known in the art (e.g.,metal such as ruthenium, osmium, rhodium, iridium, nickel, palladium,and platinum, and metal oxides such as vanadium pentoside and titaniumdioxide). For further details regarding catalytic coatings see, forexample, U.S. Pat. No. 3,441,381 (Keith et al.).

Surrounding monolith 20 is hybrid mounting system 24. Mounting system 24comprises a mat 26 of intumescent material having inserts 28 formed of aresilient, flexible, fibrous mat of essentially shot-free ceramic fiber.Inserts 28 are disposed such that at least one edge of insert 28 extendsalong a lateral edge of intumescent mat 26.

As seen in FIGS. 4A-8B, there are numerous manners in which insert 28may be positioned alongside intumescent mat 26 such that it extends outbeyond and along an edge of intumescent mat 26. FIGS. 3A and 3Billustrate an intumescent mat 26 without insert 28. FIG. 3A provides across-section view of intumescent mat 26 disposed between casing 12 andmonolith 20.

FIGS. 4A and 4B show non-intumescent inserts 28 alternating withintumescent mat 26, such that lateral edge 32 of mounting system 24presents alternating sections of intumescent and non-intumescentmaterial. As illustrated in FIG. 4B, when mounting system 24 ispositioned around monolith 20 within casing 12, non-intumescent inserts28 are preferably positioned along the portion of monolith 20 having thelargest radius of curvature. Inserts 28 are preferably positioned alongthe portion of monolith 20 having the largest radius of curvaturebecause this area corresponds to the portion of casing 12 most likely todeform under excessive pressure caused by compression of mounting system24. As noted above, in cases where the pollution control device reachesvery high temperatures, i.e., greater than about 700° C., deformation ofthe housing can occur. At these high temperatures, conventionalintumescent mounting materials greatly expand, and the resultantpressure exerted on the interior of casing 12 is very high. In addition,at such high temperatures the metal of the casing (typically stainlesssteel) begins to soften and becomes more susceptible to deformation. Bypositioning non-intumescent inserts 28 at the points most likely toexperience deformation under high temperature conditions, mountingsystem 24 generates less damaging force at high temperatures, such thatdeformation of casing 12 is greatly reduced.

FIGS. 5A and 5B show an embodiment of mounting system 24 similar to thatof FIGS. 4A and 4B. In the embodiment of FIGS. 5A and 5B, the inserts 28do not extend throughout the width of intumescent mat 26. Whenpositioned about monolith 20, non-intumescent inserts 28 are positionedin a manner like that described above for FIG. 4B.

FIGS. 6A and 6B show yet another alternative embodiment of mountingsystem 24 in which non-intumescent inserts 28 extend along the entirelength of lateral edge 34 of intumescent sheet material 26 such thatwhen mounting system 24 is disposed about monolith 20, the lateral edge34 of intumescent sheet material 26 is protected by insert 28.

Yet another embodiment of mounting system 24 is shown in FIGS. 7A and7B. In FIG. 7A, mounting system 24 is shown to include inserts 28 whichextend along the lateral edges 34 of the intumescent sheet material 26,but are offset from the intumescent sheet material to form the tab endslot configuration seen to be a laminate of intumescent material 26 andnon-intumescent material 28.

Finally, another embodiment of mounting system 24 is shown in FIGS. 8Aand 8B. The mounting system of FIGS. 8A and 8B is similar to themounting system of FIGS. 7A and 7B, but insert 28 extends only along onelateral edge 34 of intumescent sheet material 26. Insert 28 is offsetfrom intumescent sheet material 26 to form interlocking ends.

In each of the embodiments of FIGS. 4A-8B, inserts 28 may be secured tointumescent mat 26 by an adhesive tape (not shown) such as packagingtape or other suitable adhesive tape. Alternatively, inserts 28 do nothave to be secured with tape or they may be secured by other techniquessuch as stapling, stitching, and the like.

In some instances, a pollution control device may use dual monoliths,rather than a single monolith. For example, FIG. 9 shows a prior artcatalytic converter 10A which has two monoliths 20 within a metalhousing 12 and which are separated by a gap 40. In such a dual monolithconfiguration, it is known to align a metal strip 42 with the gap 40between the monoliths 20. (See, for example, German Patent DE 43 23 791A1). The metal strip is typically made from high temperature corrosionresistant metals such as Inconel and stainless steel. The metal stripcan take the form of a metal foil, corrugated metal foil, a metal fabricand the like. The metal strip 42 expands at a rate very close to that ofmetal housing 12. Because metal strip 42 expands at a rate similar tothat of housing 12, the portion of mounting mat 44 between metal strip42 and housing 12 tends to be compressed to a greater degree than theportion of mounting mat 44 between monoliths 20 and housing 12. If theportion of mounting mat 44 between metal strip and housing 12 iscompressed excessively, deformation of either housing 12 or metal strip42 can result.

As seen in FIG. 9, prior art mounting mats typically provided acontinuous layer of mounting mat 44 between metal strip 42 and housing12. As described above, this arrangement can lead to deformation ofeither housing 12 or metal strip 42. It is therefore desirable toposition a flexible, resilient fibrous insert 48 along metal strip 42between metal strip 42 and housing 12. Preferably, insert 48 is amaterial such as SAFFIL mat, available from ICI Chemicals and Polymers.As discussed above, such inserts are capable of compressing with lessforce than typically used mounting materials, such that deformation ofcasing 12 or metal strip 42 is avoided.

FIGS. 10 and 11 show alternative embodiments of the mounting system ofFIG. 9 which uses a flexible, resilient, fibrous non-intumescent insertpositioned along metal strip 42 between metal strip 42 and housing 12.In FIG. 10, metal strip 42 is inserted into routed portions 50 ofmounting mat 44, and insert 48 is secured adjacent metal strip 42 withadhesive tape 52. In FIG. 11, metal strip 42 is sandwiched betweenlayers of mounting mat 44A and 44B (such that no rotating of mountingmat material is required). Flexible, resilient, fibrous insert 48 isthen inserted between mounting mat portions 44B and secured in placewith adhesive tape 52. Either of the embodiments of FIG. 10 or FIG. 11prevent excessive compression of material between metal strip 42 andhousing 12, and thereby avoid deformation of either metal strip 42 orhousing 12.

In use, the mounting materials of the invention are disposed between themonolith and the housing in similar fashion for either a catalyticconverter or for a diesel particulate filter. This may be done bywrapping the monolith with a sheet of the mounting material, insertingthe wrapped monolith into the housing, and welding the housing. Mountingsystem 24 holds catalytic monolith 20 in place in casing 12 and sealsthe gap between catalytic monolith 20 and casing 12, to thus preventingexhaust gases from bypassing catalytic monolith 20.

Intumescent sheet material 26 comprises a resilient, flexibleintumescent sheet comprising from about 20 to 65 percent by weight ofunexpanded vermiculite flakes, such flakes being either untreated ortreated by being ion exchanged with ammonium compound such as ammoniumdihydrogen phosphate, ammonium carbonate, ammonium chloride or othersuitable ammonium compound; from about 10 percent to 50 percent byweight of inorganic fibrous material including aluminosilicate fibers(commercially available under the tradenames FIBERFRAX™ from UnifraxCo., Niagara Falls, N.Y., and CERAFIBER™ from Thermal Ceramics, Augusta,Ga.) asbestos fibers, glass fibers, zirconia-silica, and crystallinealumina whiskers; from about 3 to 25 percent by weight of binderincluding natural rubber lattices, styrene-butadiene lattices, butadieneacrylonitrile lattices, lattices of acrylate or methacrylate polymersand copolymers and the like; and up to about 40 percent by weight ofinorganic filler including expanded vermiculite, hollow glassmicrospheres and bentonite. Useful sheet materials also include thosedescribed in U.S. Pat. No. 5,523,059 (Langer) the entire content ofwhich is incorporated herein by reference.

Further, examples of intumescent sheet materials include those describedin U.S. Pat. No. 3,916,057 (Hatch et al.), U.S. Pat. No. 4,305,992(Langer et al.), U.S. Pat. No. 4,385,135 (Langer et al.), U.S. Pat. No.5,254,410 (Langer et al.), U.S. Pat. No. 4,865,818 (Merry et al.), U.S.Pat. No. 5,151,253 (Merry et al.), and U.S. Pat. No. 5,290,522 (Rogerset al.), each of which are hereby incorporated by reference. Usefulcommercially available intumescent sheets and mats includes those soldunder the INTERAM™ tradename by Minnesota Mining & Manufacturing Co. ofSt. Paul, Minn. The mounting mats typically range in thickness from 0.5to 10 mm.

Additionally, useful intumescent mounting materials include intumescentpastes such as those described in U.S. Pat. No. 5,686,039 (Merry), theentire content of which is incorporated herein by reference.

Organic binders include those described above such as natural rubberlattices, styrene-butadiene lattices, butadiene acrylonitrile lattices,and lattices of acrylate and methacrylate polymers and copolymers.

Inorganic fillers include expanded vermiculite, hollow glassmicrospheres, and bentonite. Preferably, the inorganic fillers areexpanded vermiculite.

Essentially shot-free ceramic fibers useful in forming non-intumescentinserts 28 include alumina-boria-silica fibers, alumina-silica fibers,alumina-phosphorus pentoxide fibers, zirconia-silica fibers,zirconia-alumina fibers, and alumina fibers. Useful commerciallyavailable fibers include those under the tradenames FIBERMAX fibers,available from Unifrax, SAFFIL LD fibers, available from ICI Chemicals &Polymers, ALCEN alumina fibers available from Denka, and MAFTECH fibers,available from Mitsubishi.

The fibers are typically formed by blowing or spinning using methodsknown in the industry. Preferably, the fibers are formed by spinning asol gel solution. The fibers are formed into a mat by various knownmethods including blowing the fibrous material onto a collection screenas is practiced in the nonwoven industry. A preferred non-intumescentmaterial is a polycrystalline alumina fiber, available under thetradename SAFFIL from ICI Chemicals and Polymers. The fiber ischemically resistant and may be used in selected applications up to1600° C. It is produced in a low density mat form which consists of apredominately two-dimensional random orientation of fiber resulting in amat of lamella form. The mat is essentially shot-free with a uniformfiber structure.

The lamella nature of the low density mat makes it necessary tointroduce a means for preventing delamination during handling andassembly in the pollution control device. That is, the low density matof alumina fiber is preferably physically restrained or compressedduring handling and assembly. (As used herein, “shot-free” or“essentially shot-free” refers to a fiber mat which is at least 95percent shot-free and preferably 99 percent shot-free). When compressedto a mount density of about 0.10 and 0.60 grams per cubic centimetercubed these materials have a unique ability to repeatedly undergo areduction in thickness while hot and spring back to substantially theiroriginal thickness when cooled, thus continually exerting a substantialholding force to catalytic monolith 20.

Since the fiber materials preferred for the non-intumescent inserts 28are generally available in the density range of 0.020 to 0.060 grams percentimeter, they must be compressed by about a factor of 10 when used tomount catalytic monolith 20. Mats of the non-intumescent insert materialare generally compressed and held in the compressed state to facilitatehandling of the material during assembly of catalytic converter 10.Inserts 28 may be physically compressed in a variety of manners,including the use of resin bonding, stitch bonding, or needle punching,or vacuum packing.

Resin bonding is accomplished by saturating the non-intumescent materialwith organic binders which burn off in the presences of hot exhaust gasand allow the material of insert 28 to expand during use.

Because of the low density and bulky nature of shot-free ceramic fibersand the fact that they must normally be compressed by a factor of about10 to get the desired mount density, it has also been found useful tosew or stitchbond these materials with organic thread to form acompressed mat that is closer to its ultimate thickness in use. It issometimes useful to add a very thin sheet material as a backing layer toboth sides of the fiber mat to prevent the stitches from cutting orbeing pulled through the fiber mat. The spacing of the stitches isusually from 3 to 30 millimeters so that the fibers are uniformlycompressed throughout the entire area of the mat. The organic materialsburn off when exposed to hot exhaust gas, and allow the compressed matto expand.

The shot-free ceramic fiber may also be compressed by needle-punching.Ceramic fibers by themselves are relatively brittle and not flexibleenough to be effectively needle-punched. In order to effectivelyneedle-punch a ceramic fiber mat, the mat is first overlaid with longflexible polymeric fibers, such as polypropylene fibers or polyesterfibers, that are typically about 5-10 cm long. A polymeric scrim, suchas a nylon fabric or nonwoven, is placed under the mat. The mat iscompressed between an upper and lower platen having numerous holes inthe platen. A needle board having many small barbed needles pushes theneedles through the holes. As the needles penetrate the ceramic fibermat, the barbs pull the polymeric fibers on top of the mat through thescrim, and the polymeric fibers become entangled with the scrim tophysically restrain the mat. The organic fibers and scrim will burn offwhen exposed to the elevated temperatures of use, and allow the ceramicfibers to expand.

The fiber mats can also be restrained by placing the fiber mat into anair-tight bag, evacuating the air from the bag, and sealing the bag.Atmospheric pressure restrains the mat in a compressed state until thebag is punctured or burned off when the pollution control device isheated to the temperature of use (over 300° C.).

The non-intumescent inserts 28 provide two important functions. Inserts28 have superior erosion resistance when compared to the intumescent mat26. By positioning inserts 28 along lateral edges of the intumescentmaterial which are otherwise exposed to hot exhaust gases, inserts 28serve to insulate intumescent mat 26 from the exhaust gas and therebyprevent erosion of intumescent mat 26. Although use of edge protectionmaterial is known, the prior art does not include an edge protectionsystem which can expand and compress to accommodate the changing widthof gap between monolith 20 and casing 12 under extreme temperatureconditions or if deformation of the casing occurs. Prior edge protectionmechanisms include use of a stainless steel wire screen wrapped aroundthe edges of the intumescent mat as described in U.S. Pat. No. 5,008,086(Merry), and braided or rope like ceramic (i.e., glass, crystallineceramic, or glass ceramic) fiber braiding or metal wire as described inU.S. Pat. No. 4,156,533 (Close et al.). Edge protection can also beformed from compositions having glass particles as described in EP639701A1 (Howorth et al.), EP 639702A1 (Howorth et al.), and EP 639700A1(Stroom et al.).

Inserts 28 also act as a seal between monolith 20 and casing 12. Theflexible and resilient nature of the preferred non-intumescent materialsused for inserts 28 ensure that as the pollution control device iscycled between high and low temperatures, the gap between monolith 20and casing 12 is continuously sealed, and exhaust gas is prevented frombypassing the monolith. In this manner, the efficiency of the pollutioncontrol device is maintained, and erosion of intumescent mat 26 byexhaust gas blow-by is also avoided.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofshould not be construed to unduly limit this invention. All parts andpercentages are by weight unless stated otherwise.

EXAMPLE 1

A layer of intumescent mat material (INTERAM™ Type 100 Mat, 3100 gsm(grams per square meter) available from Minnesota Mining & manufacturingCo.) measuring 6.2 cm by 30 cm was cut as shown in FIG. 5A. Strips of aresin bonded ceramic fiber mat (1200 gsm SAFFIL™ chemically bonded matavailable from ICI Chemicals & Polymers Ltd.) were cut to dimensions of1.27 cm by 9 cm and placed in the gaps cut in the intumescent mat. Thefiber mat strips were held in place with a plastic packaging tape toform a hybrid mounting mat. The hybrid mounting mat was wrapped aroundan oval ceramic monolith measuring 170 mm by 80 mm by 76 mm long(available from Corning). A second monolith was wrapped in the samemanner with a hybrid mounting mat identical to that described above. Thewrapped monoliths were mounted into a dual cavity stainless steelcatalytic converter housing. The mount density of the mounting mats wasdetermined to be 0.7 g/cc (grams per cubic centimeter) for theintumescent mat, and 0.27 g/cc for the fiber strips. The catalyticconverter containing the hybrid mounting mats was then attached to agasoline engine (Ford Motor Co. 7.5 liter displacement V-8 poweredgasoline powered internal combustion engine) at 3000 rpm/220 ft lb. Thecatalytic converter was subjected to an inlet gas temperature of 900° C.for a duration of 100 hours.

After testing, the catalytic converter assembly was disassembled andinspected. No erosion was observed on the mounting material of thehybrid mounting mat. Additionally, there was no discoloration along thewide portion of the housing over the fiber mat strips. The presence ofdiscoloration is indicative of hot exhaust gases passing between themounting mat and the metal housing. The absence of any discolorationindicates the assembly was sealed sufficiently to prevent exhaust gasesfrom flowing through the hybrid mat mounting material.

EXAMPLE 2

The mounting mats tested in this example were prepared and tested as inExample 1, except that a commercially acceptable intumescent matmaterial was used in place of the hybrid mounting mat used in Example 1.After testing, inspection of the mounting mat revealed that the mountingmat material had been eroded by the engine exhaust gas. The maximumerosion distance, i.e., the portion of the mounting mat that had erodedaway, extended 23 mm into the edge of the mounting mat. A significantamount of discoloration was also noted on the housing.

A comparison of the performance of the mounting mats tested showssignificant improvements in the performance of the hybrid mounting matof Example 1 over the performance of the non-hybrid mounting mat ofExample 2. The hybrid mounting mat resisted erosion when exposed toexhaust gases, and provided a better seal between the monolith and thehousing (as evidenced by the absence of discoloration of the housing inExample 1). Clearly, the performance of the hybrid mounting mat(Example 1) is superior to the performance of a mounting mat which doesnot utilize the fiber mat inserts (Example 2).

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A pollution control device comprising: a housing; a pollution controlelement disposed within the housing; and a mounting system disposed in agap between the pollution control element and the housing forpositioning the pollution control element within the housing and forabsorbing mechanical and thermal shock, the mounting system comprising:an intumescent mounting mat, and at least one resilient, flexible,fibrous non-intumescent insert that, independent of the intumescentmounting mat, can accommodate changes in the gap as the pollutioncontrol device is cycled between high and low temperatures, wherein theintumescent mat has a peripheral edge and the insert has a peripheraledge, and the peripheral edge of the intumescent mounting mat and theperipheral edge of the insert are juxtaposed and directly facing eachother, and the insert has a greater resiliency than the intumescentmounting mat.
 2. The pollution control device of claim 1, wherein thepollution control device has an inlet through which exhaust gases enterthe pollution control device, the mounting system has a lateral edgethat is exposed to the exhaust gases entering the pollution controldevice, and the insert forms the lateral edge of the mounting systemthat is exposed to the exhaust gases.
 3. The pollution control device ofclaim 2, wherein the insert seals the gap between the pollution controlelement and the housing so as to prevent exhaust gases from bypassingthe pollution control element, as the pollution control device is cycledbetween high and low temperatures.
 4. The pollution control device ofclaim 1, wherein the intumescent mounting mat is a sheet material. 5.The pollution control device of claim 1, wherein the at least one insertis formed of essentially shot-free ceramic fibers.
 6. The pollutioncontrol device of claim 1, wherein the pollution control element is aceramic monolithic body.
 7. The pollution control device of claim 1,wherein the insert is in a physically compressed state while disposedbetween the pollution control element and the housing.
 8. The pollutioncontrol device of claim 1, wherein the insert comprises ceramic fiberderived from a sol-gel process.
 9. The pollution control device of claim1, wherein the housing has an inlet, the mounting system has an exposedlateral edge facing the inlet, and the exposed lateral edge is exposedto exhaust gases entering the inlet.
 10. The pollution control device ofclaim 1, wherein the insert replaces a portion of the mounting mat. 11.The pollution control device of claim 10, wherein the insert and themounting mat are positioned end-to-end with respect to each other. 12.The pollution control device of claim 1, wherein the insert seals aportion of the gap between the pollution control element and the housingso as to prevent exhaust gases from bypassing the pollution controlelement through the portion, as the pollution control device is cycledbetween high and low temperatures.
 13. A pollution control devicecomprising: a housing; a pollution control element disposed within thehousing; and a mounting system disposed in a gap between the pollutioncontrol element and the housing for positioning the pollution controlelement within the housing and for absorbing mechanical vibration, themounting system comprising: an intumescent mounting mat having a lateraledge and being positioned in the gap, and at least one non-intumescent,resilient, flexible, fibrous insert positioned in the gap between thepollution control element and the housing adjacent the lateral edge ofthe intumescent mounting mat such that the non-intumescent insert canaccommodate changes in the gap as the pollution control device is cycledbetween high and low temperatures, block exposure of the mounting mat toexhaust gases entering the pollution control device and reduce erosionof the lateral edge of the mounting mat by the exhaust gases, whereinthe intumescent mat has a peripheral edge and the insert has aperipheral edge, and the peripheral edge of the intumescent mounting matand the peripheral edge of the insert are juxtaposed and directly facingeach other, and the resiliency of the non-intumescent insert is greaterthen the resiliency of the mounting mat.
 14. The pollution controldevice of claim 13, wherein the non- intumescent insert is formed ofessentially shot-free ceramic fibers.
 15. The pollution control deviceof claim 13, wherein the non-intumescent insert extends along the entirelateral edge of the mounting mat.
 16. The pollution control device ofclaim 13, wherein the non-intumescent insert expands to fill the gapbetween the housing and the pollution control element as the gapincreases, when the pollution control device is exposed to hightemperatures.
 17. The pollution control device of claim 13, wherein theinsert seals the gap between the pollution control element and thehousing so as to prevent exhaust gases from bypassing the pollutioncontrol element, as the pollution control device is cycled between highand low temperatures.
 18. A pollution control device comprising: ahousing; a pollution control element disposed within the housing; and amounting system disposed in a gap between the pollution control elementand the housing for positioning the pollution control element within thehousing and for absorbing mechanical and thermal shock, the mountingsystem comprising: an intumescent mounting mat, and at least oneresilient, flexible, fibrous non-intumescent insert that can accommodatechanges in the gap as the pollution control device is cycled betweenhigh and low temperatures, wherein the mounting mat has a peripheraledge, the insert has a peripheral edge, the peripheral edge of theinsert and the peripheral edge of the mounting mat are juxtaposed anddirectly facing each other, and the insert has a greater resiliency thanthe mounting mat.
 19. The pollution control device of claim 18, whereinthe insert seals a portion of the gap between the pollution controlelement and the housing so as to prevent exhaust gases from bypassingthe pollution control element through the portion, as the pollutioncontrol device is cycled between high and low temperatures.
 20. Amounting system for mounting a pollution control element within ahousing of a pollution control device, said mounting system comprising:an intumescent mounting mat; and at least one resilient, flexible,fibrous non-intumescent insert, wherein the intumescent mat has aperipheral edge and the insert has a peripheral edge, and the peripheraledge of the intumescent mounting mat and the peripheral edge of theinsert are juxtaposed and directly facing each other, said insert has agreater resiliency than said mounting mat, and said mounting system issuitable for absorbing mechanical and thermal shock when positioned in agap between the pollution control element and the housing, and saidinsert can accommodate changes in the gap, independent of said mountingmat, as the pollution control device is cycled between high and lowtemperatures.
 21. The mounting system of claim 20, wherein said mountingsystem has a lateral edge that is exposed to exhaust gases entering thepollution control device, when said mounting system is positioned in thegap of the pollution control device, and said insert forms said lateraledge.
 22. The mounting system of claim 20, wherein said insert and saidmounting mat are positioned end-to-end with respect to each other. 23.The mounting system of claim 20, wherein said insert replaces a portionof said mounting mat.
 24. A mounting system for mounting a pollutioncontrol element within a housing of a pollution control device, saidmounting system having a lateral edge that is exposed to exhaust gasesentering the pollution control device, when said mounting system ispositioned in a gap between the pollution control element and thehousing, and said mounting system comprising: an intumescent mountingmat having a peripheral edge; and at least one resilient, flexible,fibrous non-intumescent insert that forms said lateral edge having aperipheral edge, wherein the peripheral edge of said mounting mat andthe peripheral edge of said insert are juxtaposed and directly facingeach other, said insert has a greater resiliency than said mounting mat,said mounting system is suitable for absorbing mechanical and thermalshock when positioned in the gap between the pollution control elementand the housing, and said insert can accommodate changes in the gap asthe pollution control device is cycled between high and lowtemperatures.
 25. The mounting system of claim 24, wherein said insertis suitable for sealing the gap between the pollution control elementand the housing so as to prevent exhaust gases from bypassing thepollution control element, as the pollution control device is cycledbetween high and low temperatures.
 26. A mounting system for mounting apollution control element within a housing of a pollution controldevice, said mounting system having a lateral edge that is exposed toexhaust gases entering the pollution control device, when said mountingsystem is positioned in a gap between the pollution control element andthe housing, and said mounting system comprising: an intumescentmounting mat having peripheral edge; and at least one resilient,flexible, fibrous non-intumescent insert having a peripheral edge,wherein said mounting system is suitable for absorbing mechanical andthermal shock when positioned in the gap between the pollution controlelement and the housing, said insert can accommodate changes in the gapas the pollution control device is cycled between high and lowtemperatures; said insert has a greater resiliency than said mountingmat, and the peripheral edge of said insert and the peripheral edge ofsaid mounting mat are juxtaposed and directly facing each other.
 27. Themounting system of claim 26, wherein said insert is suitable for sealinga portion of the gap between the pollution control element and thehousing so as to prevent exhaust gases from bypassing the pollutioncontrol element through the portion, as the pollution control device iscycled between high and low temperatures.